Zoom lens system highly corrected for coma aberration

ABSTRACT

A ZOOM LENS INCLUDES FIFTEEN LENSES DEFINING FIVE LENS GROUPS INCLUDING RESPECTIVELY THE FIRST TO THE THIRD LENSES, THE FOURTH TO THE SIXTH LENS, THE EIGHTH AND NINTH LENS, THE TENTH AND ELEVENTH LENS, AND THE TWELFTH TO THE FIFTEENTH LENS, AND SATISFY THE FOLLOWING CONSITIONS:   0.7&lt;R2/R3&lt;1.1 F1/0.4&lt; F1.2 &lt;$ 1.6$N3$1.75 0.5F1$ R7 $4F1 R7&lt;0 F1$F4$0.5F1 0.05F1$R18$0.3R1 0.03F1$ R29 $0.13F1 R29&lt;0   WHEREIN R2, R3, R7, R18, AND R29 ARE THE RADII OF THE CURVATURE OF THE FIRST LENS REAR FACE, THE SECOND LENS FRONT FACE, THE FOURTH LENS FRONT FACE, THE TENTH LENS FRONT FACE AND THE FIFTEENTH LENS FROM FACE RESPECTIVELY: F1 AND F4 ARE RESULTANT FOCAL LENGTHS RESPECTIVELY OF THE FIRST THROUGH THE THIRD LENSES, AND THE NINTH AND TENTH LENSES, F1.2 IS THE RESULTANT FOCAL LENGTH OF THE FIRST AND SECOND LENSES, AND N3 IS THE INDEX OF REFRACTION OF THE THIRD LENS.

'MRCHROOM BSO-427 200M LENS SYSTEM HIGHLY CORRECTED FOR COMA ABERRATION Jam 19, 1971 YAsuo TAKAHAsH| Filed June 26. 1967 1 una/a5" INVENToR )2751/0 MMA/sw ATTORNEY United States Patent Office 3,556,641 Patented Jan. 19, 1971 3,556,641 ZOOM LENS SYSTEM HIGHLY CORRECTED FOR T COllVlyABERgIATION to i Yasuo akallashi, o o-to, span, assignor Asah Kogaku Kogyo Kabushiki Keisha, Tokyo-to, Japan, a corporation of Japan l Filed June 26, 1967, Ser. No. 648,910 Claims priority, application Japan, June 30, 1966, i1/42,820

Int. Cl. G02b 15/14, 9/60 U.S. Cl. S50-184 1 Claim Ansmcr or' THE nrscLosURE A zoom lens includes fifteen lenses defining five lens groups including respectively the'. first to the third lenses, the fourth to the sixth lens, the eighth and ninth lens, the tenth and eleventh lens, and the twelfth to the fifteenth lens, and satisfy the following conditions:

the resultant focal length of the first and second lenses, and n3 is the index of refraction of the third lens.

BACKGROUND F THE INVENTION The present invention relates ,generally to improvement in lens systems and it relates patiularly to an improved zoom lens system of long focal length which is highly corrected for coma aberration.v

With recent advances in zoom lens technique and design there has appeared a growing demand for zoom lenses of high zoom ratio, and highly corrected zoom lenses for still cameras have loirg been desired and sought after. However, the long focaln length 'zoom lenses, particularly for still cameras, which are now available or which have been heretofore piposed possess many drawbacks and disadvantages particularly in their overall optical performance over a range of effective focal lengths. While in zoom lenses of long focal length the decreased viewing angle results in a facilitated-design there is an increased aggravation of chromatic aberration which has presented an important problem.

SUMMARY or THE INVEN'noN A principal object of the present invention is to provide an improved zoom lens.

Another object of the present invention is to provide an improved zoom lens of long focal and high zoom ratio.

Still another object of the present invention is to provide an improved long focal lens high zoom ratio zoom lens system of highly corrected coma aberration.

A fui-ther object of the present invention is to provide a highly corrected long focal length zoom lensof high zoom ratio and possessing great optical efiicieiicy over its full range of adjustment.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawing which illustrates a preferred embodiment thereof.V

In a sense the present invention contemplatesl the provision QL a lens system comprising fifteen lenses consecutively dsignated as the first to the fifteenth lens and defining five lens groups consecutively designatedA as the first to the fifth lens group and including respectively the first to the third lens, the fourth to the sixth lens, the seventh and eighth lenses, the ninth and tenth lenses, andthe eleventh to the fifteenth lens and satisfying theA following conditions:

Ther-first lens group includes one negative lens and two positive lenses, the resultant type being positive; the second lens group includes two negative lenses and one positive lens, the resultant type being negative; the lthird lens group includes one negative lens and one positive lens, the resultant type being negative; the lens fourth group comprises one negative lens and one positive' lens, the resultant type being positive; and the fifth lens group comprises three positive lenses and two negative lenses, the resultant type being positive.

Thelenses are axially mounted in a `barrel in the manner conventional with zoom lenses, the first and second lens groups being oppositely axially simultaneously movable in'a predetermined mutual relationship by well known adjusting means, the movement of the first lens group being ,relatively small as compared to the movement of the second group, such movements effecting a variation in the resultant focal length of the overall lensifsystem to increase or decrease such focal length as' desired. The third'lens group is likewise axially movable? to maintain the focus of the lens system at a fixed point. The first, fourth and fifth lens groups are of the positive type and the second and lthird lens groups are of the negative type. The first, fourth, fifth, seventh, ninth, twelfth and fifteenth lenses are negative and the second, third, sixth, eighth,

tenth, eleventh, thirteenth and fourteenth lenses are positive.

Considering the conditions enumerated above, condimay occur in the short focal length range of the lens system and in addition contributes to a distortion aberration balance over the full focal length range of the lens system. Condition (S) is required for maintaining the focus of the lens system at a Ifixed position and also serves to prevent excessive lens movement. Condition (6) in cooperation with conditions (l), (2), (3) Vand (4), prevents aggravation of coma aberration inthe short focal length range of the lens system. Condition (7) prevents aggravation of Ycoma aberration with respect to positive incident light rays and light rays of low incident points. f

Under the above conditions,` in accordance with the presentinvention, a suitable correction of chromatic aberration effects an excellent balance of coma'and other aberrations, and thus the aggravation of chromatic aberration which becomes conspicuous as the focal length is increased, is prevented in a highly efficient manner.

BRIEF DESCRIPrIoN F THE DRAWINGS FIG. 1 is a longitudinal sectional view of a lens system embodying the present invention; and

FIG. 2 are sets of curves of the spherical' aberration, distortion and astigmatism of the lens system at focal lengths of 103 mm. and 584 mm. respectively.

DESCRIPTION oi= THE PREFERRED EMBODIMENTS Referring now to the drawings and particularly FIG. 1 thereof which illustrates a preferred embodiment of the present invention, the improved lens system comprises fifteen coaxially positioned lenses designated successively as lenses L1 to L15 respectively and divided into ve successive lens groups designated successively as G1 to G5 respectively.

The first lens group G1 is positive and includes the lenses L1, L2 and L3, lens L1 being negative and having a thickness d1, a refractive index nl, a front face of radius of curvature r! and a rear face of radius r2; lens L2 being positive and spaced from lens L1 a distance S1 and having a thickness d2, a refractive index n2, a front face of radius r3 and a rear face of radius r4; and lens L3 being positive andk spaced from lens L2 a distance S3 and having a thickness d3, a refractive index n3, a front face of radius f5 and a rear face of radius rs.

The second lens group G2 is negative and includes lenses L4, L5 and L6, lens L4 bein-g negativeand spaced from lens L3 a variable distance s3 and having a thickness d4, a refractive index n4, a front face of radius rq and a rear face of radius r9; lens L5 being negative and spaced from lens IA a distance s4 and having a thickness d5, a refractive index n a front face, of radius r9 and a rear face of radius rm; and L6 being positive with a front face of radius rn complementing and inY mating engagement with the rear face of lens L5, and having a thickness de, a refractive 'index n@ and a rear face of radius rn.

The fourth lens group G4 is positive and includes leneses L9 and L10, l'ensL9 being-negative and spaced from lens L8 a variable distance 'sa and having a thickness dg, a refractive index ng, a front face of radius r11 and a rear face of radius rw; a lens L10 being positive with a front face of radius rw complementing and in mating engagement with the rear face of lens L9 and having a thickness d10, a refractive index n10 and a rear face of radius rm.

The fifth lens group G5 is positive and includes lenses L11, L12, L13, L14 yand L15, lens L11 being positive. and spaced from lens L10 a distance Sm and having a thickness du, a refractive index nu, a front face of radius rn and a rear face of radius rn; lens L12 being negativeand spaced from lens L11f a distance Sn and having a thickness dlz, a refractive index nu, a front face of radius rg, and a rear face of radius ru; lens L13 being positive and spaced from lens L12 a distance Sm and having a thickness du, a refractive index nig, a front face of radius rm, and a rear face of radius fzs; lens L14 being positive and spaced from lens L13 a distance .S13 and having a thickness du; a refractive index n, a front face of radius r2, and-a rear face of radius f2s, and lens-L15 being negative and spaced from lens L14 a distance S14 and having a thieknessdl, a refractive indexing, a front face of radius r3, and a rear face of radiusrm.

It should be noted that the lens spacings are measured axially between the confronting faces of the correspondingly spaced lenses..Tl1e lens groups G-l, G2 and G3 are axially movable in the manner described above. The dimensions, relationships and parameters of the lenses are such as to satisfy .the conditions previously set forth.

The following Table I sets forth the dimensions and parameters of a specific example of the present le'ns systern. Tables II and III set forth the Seidel coefficients of the lens system adjusted for focal lengths of 103.298 millimeters and 584.163 millimeters respectively.

T'ABLE 11.-SEIDL COEFFICIENTS U=1oa.29s; EP=15s1 Sl Sz N S3 P Ss 0.'000 0. 000 0. 014 0.020 0. 734 0. 092 0. 012 0. 005 0. 137 0. 031 0. 075 0. 019 0.005 0. 115 0. 031 0. 000I 0. 000 00. 03 0. 026 0. 625 0.014 0. 017 0. 021 0. 134 0. 189 0. 007 0. 040 0. 232 0. 008 1. 385 0.025 0. 098 0. 386 0. 069 1. 786 0. 428 0. 147 0. 050 0. 275 0. 112 0. 005 0. 023 0. 104 0. 065 0. 176 0. 313 0. 224 0. 160 0. 052 0. 152 0. 268 0. 014 0. 000 0. 115 0. 006 0. 899'-v 0. 344 0.132 0.344 0. 182 0. 0481,' 0. 002 0. 000 0. 000 0. 000 0. 042 0. 091 0. 195 0. 166 0.061 15. 958 1. 000 0. 062 0. 20 0.016 2. 529. 0. 078 0. 002 0. 010 0.000 0. 080 0. 070 0. 061 0. 081 0. 125 3. 583I 0. 487 0. 006 0. 278 0. 046 14. 057 3. 601 0. 922 0. 114 0. 265 21. 108` 4. 840 1. 110 0. 193 0. 298 0. 042 0. 028 0. 019 0. 138 0. 108 19. 104 1. 188 0. 073 0. 526 t. 037 0. 252 0. 091 0. 033 0. 315 0. 102 0. 176 0. 156 0. 138 0. 300 0. 196 3. 352 1. 116 0. 371 0. 097 0. 097 38. 659 1. 568 0. 063 0. 795 0. 034 4. 748 0. 698 0. 102 0. 365 0. 066 2. 424 0. 560 0. 105 0. 120 0. 758

TABLE IIL-SElDEL COEFFICIENTS U=584.163; EP=1203] Si S2 Sa P S5 1 0.005 0. 031 0. 174 0.115 1. 607 2.-.-. 10. 684 29. 458 52. 012 0. 776 03. 207 3-- 13. 739 23. 944 41. 7% 0. 650 73. 853 4 0.000 0.005 0.040 0.149 0.730 5- 2. 630 4. 139 6. 513 0. 757 11. 440 6. 1. 268 3. 562 10. 000 0. 045 2.5. 201 7. 0. 804 2. 016 4. 705 0. 391 11. 892 8-- 0.654 0.349 0. 186 1. 559 0. 930 9 0.000 0.003 0.033 0.369 3.904 10 0. 850 0. 079 0.007 0. 294 0. 028 11 0.270 0. 390 0. 562 0. 651 1. 750 12 0.158 0. 344 0. 746 1. 950 5. 843 13 0. 008 0. 002 0. 000 0. 001 0. 000 14 0. 007 0. 091 1. 104 0. 941 1. 960 15 2. 821 1. 000 0. 354 1. 136 0. 528 16 0. 447 0. 078 0. 013 0. 058 0. 012 17 0. 014 0. 070 0. 349 0. 459 3. 999 18 0. 633 0. 487 0. 375 1. 573 1. 500 19 2. 485 3. 601 5. 219 0. 644 8. 496 20 3.732 4.840 6.277 1.094 9.560 21 0. 007 0. 028 0. 111 0. 783 3. 46S 22 3. 378 1. 188 0. 417 2. 976 1. 193 23 0. 044 0.091 0. 188 1. 785 3. 280 24 0. 031 0. 156 0. 782 2. 038 6. 293 25 0. 592 1. 116 2. 103 0. 443 3. 127 26 6. 836 1. 568 0. 359 4. 500 1. 115 27 0. 846 0. 698 0. 577 2. 012 2. 139 S M 0. 509 0. 405 0. 752 0. 681 9. 002

In Table I, r,1 are the radii of curvature of the lens faces and dn the lens spacing ad lens thicknesses are identified above, the numerators ofi rin are the indices of refraction of the corresponding subscript designated lenses and the denominators or the respective Abbe number or values thereof.

The curves shown in FIG. 2 illustrate the excellent optical properties of the lens system of the specific example of the present lens system at relatively short and long focal lengths.

While there has been described and illustrated a preferred embodiment of the present invention, it is apparent that numerous alterations, omissions and additions may be made without departing from the spirit thereof.

What is claimed is:

1. A lens system comprising fifteen lenses consecutively designated as the rst to the fifteenth with successive faces designated consecutively from the rst to the thirtieth and possessing the following parameters:

wherein r1 is the radius of curvature of ith lens face, Sn is the space between nth lens and the next successive lens, dl1 is the thickness of the'nth lens and nn is the refraction index of the nth lens, said fifth and sixth lenses, said seventh and eighth lenses'and said ninth and tenth lenses, being respectively cemented units, said rst to third lenses defining a first group, said fourth to sixth lenses defining a second group and said seventh and eighth lenses defining a third group, said second and third lens groups being axially adjustable.

References Cited UNITED STATES PATENTS 2,894,431 7/1959 Miles 350- 217 3,038,378 6/ 1962 Harris et al 350-186X 3,366,437 1/1968 Moreyame et al. S50- 186 DAVID SCHONBERG, Primary Examiner P. A. SACHER, Assistant ExaminerA U.S. Cl. X.R. S-217 

